There are three clearly distinct paths practically everywhere in the Netherlands: roads, bike paths and sidewalks.

That means the bikes, cars and pedestrians are already separated.

The mopeds/scooters (who go up to 45kmh / ~28 mph) are the only ones who don't fit in. That why they're constantly switching between roads, bike paths and sidewalks.

aren't moped expected to just drive on the main road, next to cars, and require a helmet and license plate?

Scooters are "more different".

Dutch law has two classes of 'moped'- both were originally conceived as motor-assisted pedal cycles, but in practice both are now mostly Vespa-type scooters with no option to pedal.

Both require insurance and an 'insurance plate' which is a different format from the standard licence plate seen on motorcycles. The rider must be licensed, but this can be either a car or a motorcycle licence (or a moped-specific licence which can be obtained from the age of 16, compared to 18 for cars and motorcycles).

The 'snorfiets' scooters have blue number plates, and are legally supposed to be limited to 25 km/h. The rider does not need to wear a helmet.

The 'bromfiets' scooters, with yellow number plates, are legally supposed to be limited to 45 km/h, but the rider must wear a helmet.

(In practice most scooters seem to routinely go much faster than they are supposed to be capable of)

In general, both types of scooter can use some, but not all, bike paths. A snorfiets is allowed on more bike paths than a bromfiets is- bromfietsen must ride on the main road in built-up areas.

All I can say is that the reality is that they come right at me on the bike path on the wrong side of the rode at 16+ mph. Every single time I go biking.

Whatever rules exists here exist on paper only.

I can understand. When vehicles of different cruising speeds share a roadway, the faster ones are perpetually passing. So always oncoming straight at you. It gets worse with increasing density - instead of passing occasionally, now you're passing pretty much all the time.

Its a hard problem to solve.

Ebikes and smaller scooters seem to have standarized at 16mph (25kph). That is perfectly compatible with bike lanes. A bike in a hurry can easily go over that.

Imperfectly compatible. Sure bikes can go that fast, but rarely do. The disparity in average speed results in frequent passing which is most of the problem. Head-on collisions and clipping become a thing. That's kind of the whole ball game, and why they don't get along on paths.

Almost no bikes actually go that fast, while the scooters practically always do, which is they they drive in the middle of the lanes or into oncoming traffic. Thus head on collisions etc.

It depends on your local bike culture I guess. In the US scooters go 15mph and bikes go like 12mph if you are in street clothes, ~20mph if you are in spandex.

Mixed traffic is a problem that every freakin heavy industrial site in the world has managed to solve.

We just can't solve it for cities because people have their heads up their asses and everyone wants their preferred class of traffic to get preferential treatment.

How was it solved? Consider that a designed environment is different from a built-up city with paths intended for horse-and-carriage.

By cautious rules and the ability to fire anybody who didn't follow them.

That works very well. Much better that distracted drivers and speeders.

But rules and people don't get along that well. Folks get tired and impatient. Even in the industrial environment there are expected failures per 100,000 hours etc.

Still, agreed we'd all do better with a more professional class of driver and licensing.